1. Field of the Invention
The present invention relates to a field emitter array comprising a plurality of cathode electrodes and to a manufacturing method and driving method of the same.
2. Description of the Related Art
Conventional field emitters have been disclosed by C. A. Spindt et. al in J.A. Vol. P47 pp. 5248-5263 (1976) and H. F. Gray et. al in IEDM 86 pp. 776-779 (1986).
When a field emitter is used as an electron gun for a CRT display or as a electron source for a TWT (traveling wave tube), an electron beam with a large emission volume and a narrow emission spread is required. In the above conventional field emitters, a field emitter array comprising a plurality of cathode electrodes is employed to obtain this type of electron beam.
As shown in FIG. 1, this conventional field emitter array consists of a substrate 4, an insulating film 5 having a plurality of gate holes 3 formed on the substrate 4, a gate electrode 2 formed on the insulating film 5, a plurality of cathode electrodes 1 formed on the substrate 4 in each of the gate holes 3 for emitting electrons and an anode electrode 11 formed opposite to the cathode electrodes 1 for receiving electrons emitted from the cathode electrodes 1.
When a positive voltage above a predetermined value is applied to the cathode electrode 1, an electron 6 is released from near the tip of the conical cathode electrode 1. Emission properties such as the volume of electrons 6 emitted at a fixed voltage and the minimum voltage at which electrons 6 are allowed to emit depend on the shape of the cathode electrode 1, the distance between the gate electrode 2 and the cathode electrode 1, the size of the gate hole 3 of the gate electrode 2 and such like. An emitted electron 6 is radiated to an anode electrode 11 provided opposite to the cathode electrodes 1.
In the above-mentioned conventional field emitter array comprising a plurality of cathode electrodes, the emission properties of the cathode electrode vary due to the variations in the size of the gate holes, the distance between the gate electrode and the cathode electrode and the shape of the tip of the cathode electrode. Consequently, the upper threshold applied voltage, that is, the maximum value of the voltage which can be applied between the gate electrode and the cathode electrode, varies. If a voltage exceeding the upper threshold applied voltage is applied between the gate electrode and the cathode electrode, it causes an electrical short between the two electrodes to thereby destroy the field emitter array. If the applied voltage of the field emitter array is made equal to the cathode electrode which has the lowest applicable voltage in order to avoid this, there have been the problems that the overall current density of the field emitter array is not sufficiently high and a large volume of emission can not be obtained.